One has the surname of Tennant stolen from the other Tennant.
One has a suit. One used to have a suit.
One has K9. One has Kevin.
One has a talkative assistant. One has an assistant who hardly says anything...ever.
One has a Sonic Screwdriver. One has a synthiser.
One has the Master. One has Erasure.
One can't fly the TARDIS. One can't drive???
One used to have a scarf. One used to have a No1.
One reads scripts. One corrects another person's spellings.
Everything over in 45 minutes. Everything over in 90 minutes.
Any more?...I am bored!